Atherosclerotic cardiovascular disease (CVD) is the leading cause of death in the United States. CVD originates from aberrations in normal lipid metabolism (some genetic, some lifestyle choices) that result in elevated plasma lipoproteins (principally LDLs) and/or low levels of high-density lipoproteins (HDLs). For many people, CVD is an age dependent, progressive disease that is largely undetected or ignored until an event (i.e. myocardial infarction or stroke) occurs in the later stages of disease. Therefore, current therapies focus on preventing a second event (or a primary event in high risk individuals) by reducing the circulating levels of LDLs and/or increasing HDLs. However, at a biochemical level the inability of macrophages to degrade the cholestane ring of cholesterol is a fundamental component of CVD. If macrophages had the ability to degrade cholesterol, they would not become engorged with cholesterol/cholesterol esters and elicit the maladaptive immune response that leads to the onset and progression of atherosclerosis. Recently, studies of Mycobacteria survival in human macrophages revealed a surprising observation. Mycobacteria feed on cholesterol while contained in the phagosomes of macrophages. Importantly, two enzymes that catalyze cholestane ring opening have been identified. We plan to test the hypothesis that genes encoding enzymes identified in bacteria can be humanized and used to transformation human monocyte derived macrophages, enabling the degradation of phagosome-cholesterol. The main objectives are to: 1) humanize bacterial genes encoding key ring opening enzymes, 2) develop an innovative expressions systems to regulate the expression of these genes in response to changes in cellular levels of cholesterol, and 3) characterize the production and fate of compounds generated following B-ring opening. If this paradigm-challenging hypothesis is true, the proposed studies should lead to the development of an entirely new approach for the medical management of CVD.